The pharmacokinetics and pharmacodynamics of morphine sulfate will be evaluated in 12 patients with sickle cell anemia and 12 normal volunteers matched by age, sex and race. The pharmacokinetics of both the intravenous (IV) formulation and oral (PO; extended-release) formulation of morphine will be determined in this randomized cross-over study. There will be a wash-out period of not less than seven days between either PO and IV drug administration. Pharmacodynamics will be assessed prior to 2.5 and 5 hours following PO morphine administration, and will be assessed using an experimental pain model (thermal sensitivity testing).